1. Field of the Invention
The present invention relates to a silver halide photosensitive material, and more specifically, relates to a silver halide color photosensitive material with high sensitivity and having little processing variation and improved in antistatic property and high-speed coating adoptability with little radiation fog.
2. Description of the Related Art
A demand for a silver halide color photosensitive material beco severe year by year, and high sensitivity and high image quality have been desired. In order for enhancement in sensitivity of a photosensitive material, it becomes the common practice in the art that the size of silver halide emulsion grains being photosensitive elements is increased. However, when the size of silver halide emulsion grains is increased, the number of silver halide emulsion grains is inevitably decreased so far as the content of silver halide emulsion is constant, namely, it has a defect that the number of development initiation points is decreased and the granularity is reduced. Namely, the larger the silver halide emulsion grains are, not only the more the sensitivity is improved, but also the more the granularity is deteriorated. Consequently, it is an important subject to achieve sensitivity enhancement without impairing the granularity.
In the light of the defect, when a design for increasing the number of silver halide grains per unit area is adopted, namely, when the amount of silver halide to be applied to the photosensitive material is increased, the deterioration of photographic properties occurs between manufacture and the use of the photosensitive material. Namely, fog is increased, sensitivity is lowered, granularity is deteriorated, and the diffraction of light is increased, so that the deterioration of sharpness occurs. It is the most basic and important subject in the art for improving the image quality of the photosensitive material that the sensitivity is increased without deteriorating the granularity.
Recently, a compound called “one photon two electrons sensitizer” (for example, refer to U.S. Pat. Nos. 5,747,235 and 5,747,236) and a compound called “a sensitizer capable of releasing three or more electrons per photon” (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-)2003-114487, JP-A-2003-114488 and JP-A-2003-114486) have been disclosed as partial solution for the above-described problems, and the sensitivity enhancement effect of releasing two or more electrons per photon can be obtained.
However, although the increase in the sensitivity is observed by the above-described method, its effect is not adequate. Further, an unwanted exposure trace called a static mark is occasionally generated in the photosensitive material using the above-described method and moreover, new problems of high-speed coating adaptability and the deterioration of storage stability of the photosensitive material become obvious.
The photosensitive material is brought in contact with various substances during production, photographing and development processing. For example, when the photosensitive material is in a wound-up state in the processing step, a surface layer is occasionally brought in contact with a back layer formed on the rear surface of a support. Further, the surface layer is occasionally brought in contact with stainless, a rubber roller and the like during delivery in the processing step. When the surface layer is brought in contact with these materials, the surface (a gelatin layer) of the photosensitive material is positively charged easily, and unnecessary electric discharge occurs in some cases. For this reason, an undesirable exposure trace (static mark) remains on the photosensitive material. In order to reduce the charging property of the gelatin, a compound having a fluorine atom is effective and the addition of a fluorine base surfactant is often carried out (for example, refer to JP-A's-60-128434, 3-95550 and 4-248543)
A surfactant having a fluorinated alkyl chain can carry out various surface modifications by the properties (water repellent property and oil repellent property, lubricity, antistatic property and the like) peculiar to the fluorinated alkyl chain, and is used for the surface processing of various substrates including a textile, a cloth, a carpet and a resin. When the surfactant having a fluorinated alkyl chain (hereinafter, referred to as fluorine base surfactant) is added to an aqueous medium solution of various substrates, not only a uniform film having no cissing can be formed during coating formation, but also a surfactant adsorption layer can be formed on the surface of a matrix, and the properties peculiar to the fluorinated alkyl chain can be imparted on the surface of a film. The cissing means a phenomenon in which circular or streak uncoated portions are generated due to agglomerates generated by adding various compounds to a protective layer coating solution at the production stage.
Various surfactants are also used in the photosensitive material and play an important role. The photosensitive material is usually prepared by individually coating a plurality of coating solutions containing an aqueous solution of hydrophilic colloid binder (for example, gelatin) on a support to form a plurality of layers. A plurality of hydrophilic colloid layers are often coated simultaneously at multi-layers. These layers include an antistatic layer, an under-coat layer, an antihalation layer, a silver halide emulsion layer, an intermediate layer, a filter layer and a protective layer, and various materials for expressing various functions are added to respective layers. In addition, polymer latex is occasionally contained in the hydrophilic colloid layer for improving the physical properties of the film. Further, in order to allow the hydrophilic colloid layer to contain functional compounds, such as a color coupler, an ultraviolet absorbent, an optical brightener, and a slipping agent, which are hardly soluble in water, these materials are emulsified to be dispersed as they are, or in a state in which they are dissolved in high-boiling organic solvents such as a phosphate base compound and a phthalate base compound, and are used for preparation of the coating solution in some cases. Thus, the photosensitive material is composed of various hydrophilic colloid layers in general, and it is required at its production that the coating solution containing various materials is uniformly coated at high speed without defects such as cissing and coating unevenness.
Most of fluorine base surfactants which are particularly effective for adjusting the charging property of a photosensitive material and can be most easily available have been hitherto those having a perfluorinated octyl group. Further, many of them are perfluorooctyl sulfonate which is their inherent mode, or have a structure which can be decomposed to a perfluorooctyl sulfonate compound. It has been found from recent reports that the perfluorooctyl sulfonate is possibly accumulated in the blood system of human and animals and high-level administration for a long period is toxic for experimental animals.
Consequently, there is a growing interest in discovering an alternative surfactant which does not exhibit these properties. Desirable are fluorine base surfactants which are not decomposed to perfluorooctyl sulfonate and are not accumulated less in the blood system of animals than perfluorooctyl sulfonate.
As part of solution for the problem, a telomere forming compound having a CF3(CF2)x—CH2—CH2— group cannot be decomposed to perfluorooctyl sulfonate.
It has been cleared from quantitative structural activity correlation analysis based on computer soft ware available from SRC (Syracuse Research Corporation) that the risk of in-vivo accumulation of the fluorine base surfactant having a telomere forming fluoroalkyl group, in particular, a group having 6 fluorinated carbons or less (and an ethylene group directly bonded thereof) is little, and a method of adjusting charging properties is disclosed (for example, refer to U.S. Pat. Nos. 6,232,058 and 5,837,440 and JP-A-2003-156819).
Further, the fluorine base surfactant used for the uppermost layer of the photosensitive material must be good in solubility to the coating solution of the uppermost layer and control charging without exerting a harmful influence on the uniform coating of the uppermost layer or lower image forming layer.
An additional requirement is that the surfactant of the uppermost protective layer must not adversely affect the photographic properties of the lower image forming layer.
Thus, the surfactant, in particular, the fluorine base surfactant is used as a coating aid for imparting the uniformity of a coated film or a material having a function of imparting the antistatic property of the photosensitive material.
However, these materials have not always satisfactory performance for the requisites of having the preferable charge property of the recent photosensitive material and further having processing stability and the resistance for radiation fog.